[person] An Italian chemist, born in Palermo, Sicily (1826 – 1910). Cannizzaro published a scientific work on atomic theory in 1860 that greatly increased chemists’ understanding and acceptance of Avogadro’s Law.

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[noun] A technique used to determine the age of an organic object by measuring the amount of the radioactive isotope 14C in the object. While an organism is alive, it maintains a constant amount of 14C, but once an organism dies, the 14C that was present at the time of death decays. Also called 14C-dating or radiocarbon dating.

[noun] A theoretical formulation of the most efficient thermodynamic cycle capable of converting thermal energy into work, and work into thermal energy. A defining characteristic of the Carnot Cycle is that it does not consider a change in entropy, and thus cannot exist in real practice. Like the Third Law of Thermodynamics, the Carnot Cycle serves as a reference point in measuring efficiency and entropy in heat engines.

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[person] Physicist and military engineer, born in Paris, France (1796-1832). Carnot authored Reflections on the Motive Power of Fire in 1824, which provided the first account of the theoretical workings of heat engines. Carnot's descriptions of energy transfer within heat engines provided the foundation for the Second Law of Thermodynamics. See Carnot cycle.

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[noun] The Cartesian plane, named after the mathematician Rene Descartes, is a plane with a rectangular coordinate system that associates each point in the plane with a unique pair of numbers in an ordered pair of the form (x,y). The x value is the horizontal coordinate and the y value is the vertical coordinate.

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[person] English chemist and physicist born in Nice, France (1731-1810). Cavendish's most important work was isolating hydrogen and describing its properties. He also researched electrical capacitance and used a torsion balance (now named for him) to measure the gravitational constant (G), which allowed him to calculate the mass of the Earth.

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[acronym] An abbreviation for Common Era, which is a designation for the time beginning with year 1 of the Gregorian calendar. CE is an alternative to the abbreviation AD, and the numbering of years is identical to the Anno Domini system. Compare with BCE.

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[person] Swedish astronomer born in Uppsala (1701-1744). In 1742, Celsius invented the centigrade temperature scale, using the freezing and boiling points of water as his reference temperatures. Interestingly, he defined the freezing point as 100° and the boiling point as 0°. The scale was reversed to its present form after his death. Celsius also was the first to suggest that the aurora has a magnetic cause.

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[noun] Eukaryotic cells depend on organelles known as centrioles to help organize microtubules during cell reproduction (mitosis and meiosis). The centrioles are made of tubulin arranged in a tube-like shape. The centrioles are often in a pair and are arranged at right angles to one another, forming a centrosome.

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[person] English physicist born in Bollington, Cheshire (1891-1974). Chadwick worked with Ernest Rutherford on the disintegration of atoms by bombarding them with alpha particles. He was awarded the Nobel Prize in Physics in 1935 for his discovery of the neutron.

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[person] (July 10, 1802 - March 17, 1871) Scottish author, journal editor, and publisher who was highly influential in mid-19th century scientific circles. His most famous book is Vestiges of the Natural History of Creation, published anonymously in 1844, in which he argues for transmutation, an evolutionary view of life similar to that proposed by Jean-Baptiste Lamarck, an unpopular view with both the scientific community and society in general. Charles Darwin credited Chambers with preparing people to accept the theory of evolution by natural selection.

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[person] British-American geophysicist and mathematician born in Eccles, Lancashire (1888-1970). In 1939, Chapman co-authored the classic work The Mathematical Theory of Non-Uniform Gases. The following year, he co-authored the two-volume work Geomagnetism. His most famous work in mathematics was his research in stochastic processes, for which he developed (independently of Andrey Kolmogorov) the Chapman-Kolmogorov equations.

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[person] (also known as Edwin Chargaff) Austrian-Jewish biochemist born in Czernowitz, Ukraine (then part of Austria-Hungary) in 1905. Chargaff immigrated to the United States in 1935 and died in New York City in 2002. He is best known for discovering two rules about DNA chemistry that significantly advanced the field of molecular biology. Chargaff's First Rule is that the number of adenine base units in DNA is equal to that of thymine, and the number of cytosine base units is equal to that of guanine (A = T, C = G). This was an important clue for James Watson and Frances Crick as they worked on solving the molecular structure of DNA. The Second Rule is that the composition of DNA, in terms of the relative amount of A, T, G, and C bases, varies from species to species. This was significant evidence for Oswald Avery's hypothesis that DNA carries hereditary information.

[noun] The relationship between a gas’s volume (V) and its temperature (T), which was first observed by Jacques Charles. Charles’s Law states that for a fixed amount of gas at a constant pressure, the gas’s volume increases linearly as its absolute temperature increases.

[person] A French scientist and hot-air balloonist, born in Beaugency, France (1746 – 1823). Charles invented and flew in the first hydrogen-filled balloon; while working with hot-air balloons, he observed in 1787 that a gas’s temperature and volume were linearly correlated. This relationship between temperature and volume was later named Charles’s Law by the French scientist Joseph-Louis Gay-Lussac in 1801.

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[person] (1927 - August 8, 2003) Also known as Martha C. Epstein, an American geneticist and member of the team whose experiments showed that DNA, and not protein, comprises genetic material. Chase received her PhD from the University of Southern California in 1964, but her scientific career ended shortly thereafter due to illness, and she suffered from debilitating short-term memory loss until her death in 2003.

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[noun] A process in which atoms and molecules recombine by forming or breaking chemical bonds. Chemical reactions form new products that have different chemical properties than the initial reacting material.

[noun] The movement of ions along an electrochemical gradient through a membrane. Usually, the term is applied in connection with a proton gradient to generate the energy molecule adenosine triphosphate (ATP) during cellular respiration and photosynthesis.

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[noun] Compounds consisting of carbon, chlorine, fluorine, and sometimes hydrogen once used widely as aerosol propellants and refrigerants. lso known as CFCs. The realization that chlorofluorocarbons cause depletion of the stratospheric ozone layer led to a sharp decrease in their use mandated by the Montreal Protocol in 1989.

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[noun] Chromatin is the substance inside of the cell's nucleus and it consists of DNA, proteins (primarily histones), and chromosomal RNA. The principal function of chromatin is to package DNA by folding it up into a compact form that, when stained with a dye, can be seen as individual chromosomes. Chromatin is only found in eukaryotic cells.

[noun] Generally, movement within a system. 1. [Atmospheric] the movement of air masses within the troposphere, driven by the redistribution of energy from the sun and the rotation of the Earth. 2. [Oceanic] the movement of water in Earth’s oceans driven by surface winds, Earth’s rotation, and density differences.

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[noun] A person (usually a volunteer or student) who is not a professional scientist but contributes to scientific research. Some citizen scientists assist researchers in analyzing large datasets. Others help by reporting things like rainfall or bird species observed in their backyard. Successful projects, such as those run by the Cornell Lab of Ornithology and the National Weather Service, often rely on volunteers in many locations making repeated observations over time. This can allow citizen science projects to achieve results that a single scientist or small team of researchers could not.

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[person] (aka Rudolph Gottlieb) Physicist and mathematician, born in Koszalin, Poland (1822-1888). Clausius authored On the Moving Force of Heat and the Laws of Heat which may be Deduced Therefrom in 1850. This text explored the mechanical theory of heat and the contradictions between the Carnot cycle and the conservation of energy. In 1865, Clausius provided the first description of, and mathematical formula for entropy.

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[noun] Climate describes the average and patterns of a particular area’s weather over time. Climate includes such elements as temperature, precipitation, humidity, sunshine, wind velocity, and other measures of the weather. Weather, on the other hand, is the description of short-term atmospheric changes.

[noun] The interaction of a molecule with other molecules of the same substance due to intermolecular forces such as hydrogen bonding. For example, rain falls in droplets due to cohesive forces between water molecules.

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[noun] A type of breakage that produces a smooth, curved surface. Conchoidal fracture occurs when a substance has uniform strength in all directions and no pre-existing planes of atomic weakness. This generally occurs in two types of substances: minerals like quartz whose atomic structure consists of equally strong bonds in all directions, and volcanic glass, called obsidian, which has no definitive crystal structure.

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[noun] A measurement of a substance’s ability to transmit (or conduct) heat, sound, or electricity. For example, copper exhibits high conductivity in relation to the transfer of heat or electricity.

In aquatic science, conductivity is a measurement of water’s ability to conduct electricity. Along with salinity (the measurement of salt dissolved in a volume of water), conductivity provides information on what kinds of dissolved solids are in the water. Water with a high concentration of inorganic salts, for example, will conduct electricity much faster than water with a lower concentrations.

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[noun] A type of interval estimate commonly used by scientist to report a plausible range of values for a population parameter based on a subsample dataset. The confidence interval is named after the fact that its construction relies on choosing a confidence level that reflects the degree of uncertainty associated with the estimation. The confidence level represents the percentage of confidence intervals that can be expected to include the true population parameter if all possible confidence intervals were calculated from all possible subsamples.

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[noun] In statistics, the confidence level reflects the degree of uncertainty associated with a parameter estimation, particularly the calculation of a confidence interval. Higher confidence levels reflect less uncertainty while lower confidence levels reflect more uncertainty. Scientists often use a 95% confidence level.

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[noun] Careful use of natural resources to minimize waste or damage to the natural world and to maintain natural resources for long-term human use. Historically, conservation has been contrasted with preservation – a strategy of setting aside resources and wild areas for protection from human impacts. In common usage, though, conservation has come to mean any activity that protects or restores the natural environment.

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[noun] An interdisciplinary branch of science focused on understanding and maintaining Earth's biodiversity and the natural processes that create and sustain it. Conservation biologists study the impacts that humans have on biological diversity (variety) from the genetic level to the whole ecosystem level. They also develop practical ways to protect and restore that diversity.

While it has roots in the older field of ecology, conservation biology is a young scientific discipline. It emerged as its own recognized field of study in the 1980s, though wildlife managers in Australia and Europe had been using the term and practicing some of its tenets (principles) for several decades.

Biologist and founder of the Society for Conservation Biology Michael Soulé wrote one of the first formal explanations of the field in his 1985 paper "What is conservation biology?" Soulé and other early supporters called it a "crisis discipline" because it arose in response to concern over extinction and global loss of biodiversity.

At its core, conservation biology is an applied science with certain goals and values built into it. Like all scientists, conservation biologists seek knowledge about the natural world. But they also suggest ways to apply that knowledge to a real-world problem: biodiversity loss.

Modern conservation biologists draw on wide-ranging disciplines like genetics, physiology, forestry, social science, and many others. They employ a number of tools and approaches in their efforts to study and protect biodiversity. Some of the most common are nature reserves designed to protect species and their habitats and captive breeding programs to help boost wild populations.

Conservation biologists fill many roles, including academic researchers, government wildlife managers and land use planners, breeders at zoos and aquaria, and scientists and advocates working for non-profit groups.

To learn more about the profession and its history, download Soulé's classic paper "What is conservation biology?" (http://www.michaelsoule.com/resource_files/85/85_resource_file1.pdf) and visit the Society for Conservation Biology (http://www.conbio.org). To learn about global efforts to conserve biodiversity, explore the United Nations Convention on Biological Diversity (http://www.cbd.int).

[noun] The uppermost layer of the Earth that forms the continents. Unlike oceanic crust, continental crust is created and destroyed very slowly, so there is some continental crust on the Earth as old as 4 billion years. Continental crust ranges from 10-70 km thick and is composed primarily of granite.

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[noun] The theory proposed in 1915 by Alfred Wegener, a German geophysicist and meteorologist. The theory stated that the continents had once been joined into one “supercontinent,” called Pangaea. About 200 million years ago, Pangaea broke apart and the continents drifted to their present positions. Wegener based his theory on the similarity of fossils and rock types on the east coast of South America and the west coast of Africa. The theory was widely ridiculed at the time because Wegener had not proposed a driving force for such drift.

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[noun] In science, a control is a system for which the expected change or outcome is well known and is measured or observed for the purpose of comparing it to a treatment group in scientific research. The control is used as a standard to compare or quantify change in the treatment. For more information, see Experimentation in Scientific Research.

[noun] An argument, disagreement, or difference of opinion that involves many people. A true scientific controversy involves a sustained debate within the broader scientific community with a significant number of people actively engaged in research that addresses the issue over time.

[person] American paleontologist, born near Philadelphia, Pennsylvania (1840-1897). Cope was a prolific writer and very successful fossil-hunter, publishing over 1200 papers during his career. He developed Cope's law, stating that mammalian species become larger over time. Cope was especially interested in the natural history of reptiles and amphibians, publishing Bactrachian of North America and The Crocodilians and Snails of North America. Copeia, the leading scientific journal in the field of herpetology, is named in his honor.

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[person] (Mikolaj Kopernik or Nicolaus Koppernigk) Polish astronomer born in Torun in the Royal Prussia region of the Kingdom of Poland (now Poland) (1473–1543). Copernicus was the first European scientist to provide scientific evidence for a heliocentric view of the solar system. In 1543, Copernicus published De revolutionibus orbium coelestium, often considered the origin of the Scientific Revolution.

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[noun] Correlation, as measured by the correlation coefficient, provides a measure of the strength and direction of a linear relationship between two random variables. While there are many measures of correlation, among the best known is the Pearson product-moment correlation, which ranges from -1 to 1. A correlation coefficient close to -1 indicates a strong negative correlation; a correlation coefficient close to 0 indicates little correlation; and a correlation coefficient close to 1 indicates a strong positive correlation.

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[person] (September 10, 1864 - February 14, 1933) German botanist and geneticist. He is remembered for his independent discovery of the principles of heredity and for his rediscovery of Gregor Mendel's earlier work on that subject. Correns also discovered cytoplasmic inheritance, that is, the influence of extra-chromosomal factors on phenotype. Unfortunately, most of Correns' work was unpublished and was destroyed when the Allies bombed Berlin in 1945.

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[person] (1485 – December 2, 1547) Spanish conquistador. In the early 16th century, he led the expedition that caused the fall of the Aztec Empire, bringing much of mainland Mexico under the rule of the King of Castile. Cortes used the very effective strategy of making allies with some of the native tribes, and using these allies to attack other native tribes. The King of Castile awarded Cortes the title of Marqués del Valle de Oaxaca for his success in overthrowing the Aztec Empire.

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[noun] A very strong chemical bond formed by the sharing of a pair of electrons. Multiple covalent bonds can be formed when multiple pairs of electrons are shared between atoms. Covalent bonds are generally characterized in two types, polar and nonpolar covalent bonds. Compare to ionic bond and hydrogen bond.

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[noun] A molecule held together by covalent bonds, that is, pairs of electrons shared between atoms. Covalent molecules are true chemical molecules whose interaction with other molecules is influenced by whether a polar molecule or non-polar molecule is formed.

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[person] English molecular biologist, physicist, and neuroscientist, most noted for being one of the co-discoverers of the structure of the DNA molecule in 1953. He later contributed to the successful deciphering of the genetic code of DNA.

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[acronym] Stands for "clustered regularly interspaced short palindromic repeats," often associated with "CRISPR-associated sequences" or Cas. Component of an adaptive immune system that protects prokaryotes against viruses. Researchers are using modified CRISPR-Cas systems to edit the genomes of organisms. The CRISPR system most commonly used in genome editing is CRISPR-Cas9.

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[noun] In the context of the US Endangered Species Act, the geographic area that is essential to conserving a threatened or endangered species. The US Fish and Wildlife Service designates critical habitat in order to protect areas where an endangered species is found and areas with key physical and biological characteristics that will be needed as the species recovers.

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[noun] The uppermost 5-70 km of the Earth. There are two types of crust: continental and oceanic. Continental crust ranges from 10-70 km thick and has a composition approximating that of granite. Oceanic crust, on the other hand, is approximately 5 km thick and has a composition similar to basalt, making it significantly denser than continental crust.

[noun] A solid of defined shape that is bound by plane surfaces (facets) that intersect at characteristic angles. The shape of a crystal is defined by the bonding and/or interaction between atoms, ions, or molecules that make up the solid. The substances, planar angles, and defects in a crystal affect the electrical and optical properties (including color) of the crystal.

[adjective] Having a regular, lattice-like arrangement of atoms or molecules. Crystalline solids melt at a precise melting point and break along specific planes and at specific angles defined by the crystal’s geometry.

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[noun] The process through which crystals form, resulting in the change from a liquid or vapor to a solid. Crystallization can happen in two basic ways:
1. By lowering the temperature of a melted material like magma or water, atoms and ions start to aggregate into crystals, forming solid rock or ice. This can also happen from a vapor, as is the case with the formation of snowflakes, but it is much less common.
2. By evaporating water from a solution, the saturation point of the water is reached and a solid begins to precipitate out as crystals (for example, salt flats in the desert have been precipitated out of lakes that dried up).

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[person] French-Polish physicist and chemist born in Warsaw (1867–1934). Curie was the Head of the Physics Laboratory at the Sorbonne. Working with her husband, Pierre Curie, and inspired by Becquerel's discovery of radiation, Curie isolated and named the element polonium. She also developed techniques for isolating radium from radioactive residues in order to study its properties. Curie was awarded, with Pierre, half a Nobel Prize in Physics in 1903, for their study of Becquerel radiation. After her husband's death in 1906, she succeeded him as Professor of General Physics, and was the first woman to hold the post. In 1911, she was awarded a Nobel Prize in Chemistry for her work in radioactivity.

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[person] French physicist born in Paris (1859-1906 CE). Pioneer in the fields of crystallography, magnetism, and piezoelectricity, he shared the 1903 Nobel Prize in Physics with his wife Marie Curie and with Henri Becquerel for research on the "radiation phenomena."

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[noun] A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The role of cytoplasm within the cell is to move materials around and to dissolve cellular waste. It is the primary site for chemical activity in the cell.

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[noun] The fluid portion of the cytoplasm that is in every animal and plant cell. It surrounds all of the organelles of a cell. Most of the cell's metabolism takes place in the cytosol. It is made of water and fibrous proteins that play an important role in signal transduction pathways and act as intracellular receptors.